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Publication numberUS4578623 A
Publication typeGrant
Application numberUS 06/612,643
Publication dateMar 25, 1986
Filing dateMay 21, 1984
Priority dateMay 26, 1983
Fee statusPaid
Also published asDE3419668A1, DE3419668C2, DE3448312C2
Publication number06612643, 612643, US 4578623 A, US 4578623A, US-A-4578623, US4578623 A, US4578623A
InventorsSeiichi Tsukutani, Naoki Nakada
Original AssigneeMatsishita Electric Industrial Co.
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Burn-out preventive circuit for commutatorless motor
US 4578623 A
Abstract
A burn-out preventive circuit for a commutatorless motor comprises drive windings of two phases, driving power transistors connected in series with the drive windings respectively, a position detecting element detecting the angular position of rotation of a permanent magnet rotor for alternately turning on the driving power transistors, and a protective circuit detecting a counter-electromotive force induced in the drive windings during rotation of the permanent magnet rotor for interrupting energization of the drive windings when the detected counter-electromotive force is lower than a predetermined level or zero.
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Claims(10)
We claim:
1. A burn-out preventive circuit for a commutatorless motor comprising half-wave driven drive windings of two phases, driving power transistors connected in series with said drive windings respectively, position detecting means connected at its output terminal to the bases of said driving power transistors directly or indirectly for alternately turning on said driving power transistors depending on the angular position of rotation of a permanent magnet rotor, a power transistor constituting part of protective means connected in series with said drive windings, and diodes connected at their anodes to the negative power supply terminal side of said drive windings and at their cathodes to the base of said power transistor through a resistor, said power transistor being turned off when the counter-electromotive force induced in the non-energized one of said drive windings while the other is being energized is lower than the predetermined level or zero, thereby interrupting energization of said latter drive winding.
2. A burn-out preventive circuit as claimed in claim 1, wherein a starting compensation circuit is connected between the collector and the base of said power transistor to maintain said power transistor in its on state until the counter-electromotive force is induced in one of said drive windings which is not energized at the time of starting the motor.
3. A burn-out preventive circuit as claimed in claim 2, wherein said starting compensation circuit includes a series circuit of a resistor and a capacitor.
4. A burn-out preventive circuit for a commutatorless motor comprising half-wave driven drive windings of two phases, driving power transistors connected in series with said drive windings respectively, a first transistor connected in parallel with the series circuits of said drive windings and said driving power transistors and connected at its base to the cathodes of diodes connected at their anodes to the negative power supply terminal side of said drive windings respectively, said first transistor being turned off when the counter-electromotive force is induced in the non-energized one of said drive windings while the other is being energized, but turned on when the induced counter-electromotive force is lower than the predetermined level or zero, position detecting means connected at its output terminal to the bases of said driving power transistors directly or indirectly for alternately turning on said driving power transistors depending on the angular position of rotation of a permanent magnet rotor, and a second transistor having its base connected to the collector of said first transistor and its collector connected to said position detecting means, said second transistor being turned on when said first transistor is turned on thereby interrupting the current supplied to the base of said driving power transistor connected in series with the energized one of said drive windings, so that said specific driving power transistor is turned off to interrupt energization of said specific drive winding.
5. A burn-out preventive circuit as claimed in claim 4, wherein a starting compensation circuit is connected between the collector and the base of said second transistor to maintain said second transistor in its off state until the counter-electromotive force is induced in one of said drive windings which is not energized at the time of starting the motor.
6. A burn-out preventive circuit as claimed in claim 5, wherein said starting compensation circuit includes a series circuit of a resistor and a capacitor.
7. A burn-out preventive circuit for a commutatorless motor comprising drive windings of at least two phases, switching means connected in series with said drive windings respectively, position detecting means detecting the position of a permanent magnet rotor for alternately turning on said switching means, and protective means detecting a counter-electromotive force induced in said drive windings during rotation of said permanent magnet rotor for interrupting energization of said drive windings when the detected counter-electromotive force is lower than a predetermined level or zero, said protective means including a power transistor connected in series with said drive windings, diodes connected at their anodes to the negative power supply terminal side of said drive windings respectively, and a resistor connected between the base of said power transistor and the cathodes of said diodes, said power transistor being turned off when the counter-electromotive force induced in the non-energized one of said drive windings while the other is being energized is lower than the predetermined level of zero, thereby interrupting energization of said latter drive winding.
8. A burn-out preventive circuit as claimed in claim 7, wherein said position detecting means includes a Hall element or a Hall IC.
9. A burn-out preventive circuit for a commutatorless motor comprising drive windings of at least two phases, switching means connected in series with said drive windings respectively, position detecting means detecting the position of a permanent magnet rotor for alternately turning on said switching means, and protective means detecting a counter-electromotive force induced in said drive windings during rotation of said permanent magnet rotor for interrupting energization of said drive windings when the detected counter-electromotive force is lower than a predetermined level or zero, said protective means including diodes connected at their anodes to the negative power supply terminal side of said drive windings respectively, a first transistor connected at its base to the cathodes of said diodes, said first transistor being turned off when the counter-electromotive force is induced in the non-energized one of said drive windings while the other is being energized, but turned on when the induced counter-electromotive force is lower than the predetermined level or zero, and a second transistor having its base connected to the collector of said first transistor and its collector connected to said position detecting means, said second transistor being turned on when said first transistor is turned on thereby decreasing or interrupting the current supplied to the base of said switching means connected in series with the energized one of said drive windings.
10. A burn-out preventive circuit as claimed in claim 9, wherein said position detecting means includes a Hall element or a Hall IC.
Description
BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a commutatorless motor of the half-wave driven type provided with switching means that is on-off controlled depending on the angular position of rotation of a permanent magnet rotor, and more particularly to a burn-out preventive circuit for use in such a commutatorless motor for limiting the supply of a large current to the drive windings of the motor when the rotor is locked against rotation, thereby preventing burn-out of the drive windings.

2. Description of the Prior Art

As one of the prior art methods for preventing burn-out of the drive windings of a commutatorless motor when its rotor is locked against rotation due to an externally imparted force, a current limiting method is most frequently employed and commonly known which utilizes the fact that heat is generated from the drive windings or from a thermistor due to a large current appearing in the event of locking of the rotor. However, the prior art method utilizing the generated heat for preventing burn-out of the drive windings of the motor has had the problem of a slow response. Also, such a preventive device has been difficult to design especially when the motor is of the heavy-loaded type since the value of current in a locked condition does not appreciably change from that supplied under normal operation.

SUMMARY OF THE INVENTION

With a view toward overcoming these prior art problems, it is a primary object of the present invention to provide a burn-out preventive circuit which operates quickly and reliably to prevent burn-out of the drive windings when used in a commutatorless motor.

The present invention is featured by the fact that a counter-electromotive force induced in the drive windings of a commutatorless motor is detected to prevent burn-out of the drive windings in the event of locking of the rotor against rotation. That is, in the case of the drive windings of a commutatorless motor of the half-wave driven type, there is a time region in which no current is supplied thereto during rotation of the motor. In this time region, a counter-electromotive force is induced in the drive windings under the influence of the magnet of the permanent magnet rotor. However, such a counter-electromotive force is not induced in that one of the drive windings which is not under energization, when the motor is locked against rotation due to an externally imparted force. It is the burn-out preventive circuit of the present invention which discriminates the presence or absence of such a counter-electromotive force thereby limiting the current supplied to the drive windings of the motor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of an embodiment of the burn-out preventive circuit of the present invention applied to a commutatorless motor.

FIG. 2 is a circuit diagram of another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the present invention will now be described in detail with reference to FIG. 1. Referring to FIG. 1, two-phase drive windings L1 and L2 constitute part of a stator of a commutatorless motor of the half-wave driven type and are disposed opposite to a permanent magnet rotor (not shown). Position detecting means H such as a Hall element or a Hall IC is connected across power supply terminals through a resistor R1. This position detecting means H is disposed at a position at which it is magnetically coupled to the permanent magnet rotor to detect the angular position of rotation of the permanent magnet rotor, and a rotation position signal of high or low level is generated from its output terminal depending on the angular position of rotation of the permanent magnet rotor. A transistor Tr1 is connected at its collector to the positive power supply terminal through a resistor R2, at its emitter to the negative power supply terminal through a resistor R3 and at its base to the output terminal of the position detecting means H. Driving power transistors Tr2 and Tr3 constitute switching means for switching over the current supplied to the drive windings L1 and L2. The transistor Tr2 is connected at its collector to the positive power supply terminal side through the drive winding L1, at its emitter to the negative power supply terminal and at its base to the emitter of the transistor Tr1. The transistor Tr3 is connected at its collector to the positive power supply terminal side through the drive winding L2, at its emitter to the negative power supply terminal and at its base to the collector of the transistor Tr1 through a diode D3. Protective means P detects the counter-electromotive force induced in the drive windings L1 and L2 and acts to interrupt the current supplied to the drive windings L1 and L2 when the detected counter-electromotive force is lower than a predetermined level or zero. This protective means P includes a power transistor Tr4 connected at its collector to the positive power supply terminal and at its emitter to the drive windings L1 and L2 , a pair of diodes D1 and D2 connected at their anodes to the negative power supply terminal side of the drive windings L1 and L2 respectively, and a resistor R4 connected between the base of the power transistor Tr4 and the cathodes of the diodes D1 and D2. Capacitors C1 and C2 are connected in parallel with the collector and emitter of the driving power transistors Tr2 and Tr3 respectively to suppress a spike voltage generated in the drive windings L1 and L2 during switching of the transistor Tr2 or Tr3. The diode D3 is connected at its anode to the connection point of the resistor R2 and the collector of the transistor Tr1 and at its cathode to the connection point of the resistor R6 and the base of the driving power transistor Tr3 for preventing turning-on of the driving power transistor Tr3 when the transistor Tr1 is turned on. A series circuit of a resistor R5 and a capacitor C3 is connected between the base and the collector of the power transistor Tr4. This series circuit acts as a starting compensation circuit which maintains the power transistor Tr4 in its on state until a counter-electromotive force is induced in the drive winding which is not energized at the time of starting the motor.

In the burn-out preventive circuit having the structure above described, the diode D1 or D2 selects the voltage of the driving power transistor Tr2 or Tr3 associated with the drive winding L1 or L2 which is not low energized, and such a voltage is applied to the base of the transistor Tr4. When now the output of high level appears from the output terminal of the position detecting means H, the transistor Tr1 is turned on, and current is supplied to the base of the driving power transistor Tr2 to energize the drive winding L1. At this time, a counter-electromotive force is induced in the drive winding L2, which is not energized now, to apply a bias voltage to the base of the power transistor Tr4 through the diode D2 and resistor R4, so that the base voltage of the transistor Tr4 becomes higher than the emitter voltage to maintain the transistor Tr4 in its on state. At this time, the resistor R4 acts to regulate the base current of the transistor Tr4.

Then, when the output of the position detecting means H turns into its low level, the transistor Tr1 is turned off, and base current is supplied to the driving power transistor Tr3 through the resistor R2 and diode D3 to energize the drive winding L2. A counter-electromotive force is similarly induced in the other drive winding L1 to apply a bias voltage to the base of the power transistor Tr4 through the diode D1 and resistor R4, so that the transistor Tr4 is maintained in its on state. Thereafter, the drive windings L1 and L2 are alternately energized in the manner above described, thereby causing rotation of the permanent magnet rotor.

Suppose then that the permanent magnet rotor is locked against rotation when, for example, the drive winding L1 is being energized. In such an event, no counter-electromotive force is induced in the other drive winding L2 which is not energized, and a bias voltage is not applied to the base of the transistor Tr4. Consequently, the transistor Tr4 is turned off, and no current is supplied to the drive winding L1 thereby preventing burn-out of the drive winding L1. According to this burn-out preventive circuit, release of the permanent magnet rotor from the locked condition would not re-start the motor unless the power supply voltage is applied again. However, when a resistor of the large power consuming type is connected between the collector and the emitter of the transistor Tr4, manipulation for re-application of the power supply voltage for re-starting the motor is unnecessary, and the resistor R5 and capacitor C3 are also unnecessary.

FIG. 2 shows another embodiment of the present invention or a modification of the embodiment shown in FIG. 1. In FIG. 2, the protective means P includes diodes D1, D2, D4, D5, small signal transistors Tr5, Tr6, and resistors R6, R7.

Referring to FIG. 2, the transistor Tr5 is connected at its emitter to the positive power supply terminal, at its base to the negative power supply terminal through the diode D4 and resistor R6, and at its collector to the base of the transistor Tr6 through the resistor R7. The transistor Tr6 is connected at its collector to the connection point of the resistor R2 and the collector of the transistor Tr1 and at its emitter to the negative power supply terminal. The diode D5 is connected at its anode to the cathodes of the diodes D1, D2 and at its cathode to the connection point of the diode D4 and the resistor R6. The diode D4 is disposed in the same polarity as that of the diodes D1 and D2 so that the base voltage of the transistor Tr5 may not exceed the emitter voltage thereby destroying the transistor Tr5. Further, this diode D5 is provided for the purpose of attaining a voltage balance in the arrangement in which the diode D4 is coupled to the base of the transistor Tr5. The resistor R6 is provided for regulating the base current of the transistor Tr5.

In FIG. 2, a capacitor C4 connected to the base of the transistor Tr6 and a resistor R8 providing the discharge circuit of the capacitor C4 constitute a starting compensation circuit which prevents the transistor Tr6 from being turned on by base current supplied to the transistor Tr6 through the transistor Tr5 and resistor R7, until a counter-electromotive force is induced in the drive winding which is not energized at the time of starting the motor. More precisely, at the motor starting time, the transistor Tr5 is turned on, and base current tends to be supplied to the transistor Tr6. At this time, however, charge current is supplied to the capacitor C4 to maintain the transistor Tr6 in its off state. Thus, the drive windings L1 and L2 are alternately energized depending on the level of the output of the position detecting means H thereby causing rotation of the permanent magnet rotor. When the rotor is placed under rotation, the counter-electromotive force is induced in the drive winding L1 or L2, and the transistor Tr5 is turned off for the reason described later thereby inhibiting the transistor Tr6 from being turned on. The voltage charged in the capacitor C4 is discharged through the resistor R8 when the transistor Tr5 is turned off.

The operation of the circuit shown in FIG. 2 will now be described. Suppose now that the output of the position detecting means H is in its high level. Then, the transistor Tr1 is turned on, and the driving power transistor Tr2 is turned on to energize the drive winding L1. A counter-electromotive force is induced in the non-energized drive winding L2 to apply a reverse bias voltage to the base of the transistor Tr5 through the diodes D2 and D5, so that the transistors Tr5 and Tr6 are maintained in their off state. Then, when the output of the position detecting means H turns into its low level, the transistor Tr1 is turned off, and base current is supplied to the power transistor Tr3 through the resistor R2 and diode D3, thereby turning on the transistor Tr3 to energize the drive winding L2. At this time, a counter-electromotive force is similarly induced in the other drive winding L1 to apply a reverse bias voltage to the base of the transistor Tr5 through the diodes D1 and D5, thereby maintaining the transistors Tr5 and Tr6 in their off state. Thereafter, repetition of similar operation alternately energizes the drive windings L1 and L2 to cause rotation of the permanent magnet rotor.

Suppose that the permanent magnet rotor is locked against rotation while, for example, the drive winding L1 is being energized. In such a case, no counter-electromotive force is induced in the other drive winding L2 which is not energized now, and no reverse bias voltage is applied to the transistor Tr5. Consequently, the voltage drop due to the resistance included in the drive winding L1 and across the diodes D1 and D5 becomes larger than that across the base-emitter circuit of the transistor Tr5 and across the diode D4, and the base potential of the transistor Tr5 is lowered to turn on the transistor Tr5. Consequently, charging current is supplied through the resistor R7 to the capacitor C4 until the capacitor C4 is completely charged. The transistor Tr6 is now turned on, and current flows now to the transistor Tr6 through the resistor R2, so that no current flows through the transistor Tr1. Consequently, the power transistor Tr2 is turned off to interrupt the current supplied to the drive winding L1 thereby preventing burn-out of the drive winding L1 due to the continuous energization. Such a protective operation takes place similarly when the permanent magnet rotor is locked against rotation during energization of the drive winding L2.

It will be apparent from the foregoing detailed description that, according to the present invention, a counter-electromotive force induced in the drive windings of a commutatorless motor is detected to control energization of the drive windings, so that objectionable burn-out of the drive windings in the event of locking of the motor can be reliably prevented by the protective means which operates at a very high response speed.

Patent Citations
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US4169990 *Jun 1, 1977Oct 2, 1979General Electric CompanyElectronically commutated motor
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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4694371 *May 3, 1985Sep 15, 1987Ebm Elektrobau Mulfingen Gmbh & Co.Protection circuit for stalling protection in commutatorless direct current motors
US4814675 *Jun 9, 1988Mar 21, 1989ValeoDevice limiting the power supply current for a direct current motor equipped with such a device
US4896089 *Jan 31, 1989Jan 23, 1990General Electric CompanyFault management system for a switched reluctance motor
US4947091 *Oct 30, 1989Aug 7, 1990Matsushita Electric Industrial Co., Ltd.Device for preventing a coil of a brushless motor from burning
US5317244 *Aug 6, 1992May 31, 1994Sharp Kabushiki KaishaMotor control unit provided with anti-burning device
US5363024 *Sep 24, 1992Nov 8, 1994Fujitsu LimitedD.C. fan control circuit device for linearly variable cooling
US5434488 *Dec 16, 1992Jul 18, 1995Matsushita Electric Industrial Co., Ltd.Device for preventing the burning of a coil for a brushless motor and capable of controlling the speed of the motor
US5616995 *Mar 9, 1995Apr 1, 1997General Electric CompanySystems and methods for controlling a draft inducer for a furnace
US5675231 *May 15, 1996Oct 7, 1997General Electric CompanySystems and methods for protecting a single phase motor from circulating currents
US5676069 *Nov 3, 1995Oct 14, 1997General Electric CompanySystems and methods for controlling a draft inducer for a furnace
US5680021 *Jun 7, 1995Oct 21, 1997General Electric CompanySystems and methods for controlling a draft inducer for a furnace
US5682826 *Apr 28, 1995Nov 4, 1997General Electric CompanySystems and methods for controlling a draft inducer for a furnace
US5696430 *Jun 6, 1995Dec 9, 1997General Electric CompanyCircuit, motor, and method generating a signal representing back EMF in an energized motor winding
US5825597 *Sep 25, 1996Oct 20, 1998General Electric CompanySystem and method for detection and control of circulating currents in a motor
US6060848 *Jan 15, 1999May 9, 2000Plaset SpaSystem for controlling a brushless electric motor
US6731086 *Apr 26, 2002May 4, 2004Rohm Co., Ltd.Motor driving device
US6930867 *Sep 30, 2002Aug 16, 2005Sunonwealth Electric Machine Industry Co., Ltd.Thermally suppressing circuit for restarting a locked motor
EP0540417A1 *Oct 28, 1992May 5, 1993Valeo Thermique HabitacleOverload protection device for electronic commutated electric motor
EP0930697A1 *Jan 13, 1999Jul 21, 1999Plaset S.r.l.A system for controlling a brushless electric motor
WO1999037015A1 *Jan 15, 1999Jul 22, 1999Plaset SpaA system for controlling a brushless electric motor
Classifications
U.S. Classification318/400.21
International ClassificationH02P6/12, H02P1/16, H02H7/093, H02P6/00
Cooperative ClassificationH02P1/16, H02P6/00, H02H7/093
European ClassificationH02H7/093, H02P1/16, H02P6/00
Legal Events
DateCodeEventDescription
Sep 15, 1997FPAYFee payment
Year of fee payment: 12
Aug 9, 1993FPAYFee payment
Year of fee payment: 8
Aug 14, 1989FPAYFee payment
Year of fee payment: 4
Sep 2, 1986CCCertificate of correction
Jul 17, 1984ASAssignment
Owner name: MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD., 1006, OA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNORS:TSUKUTANI, SEIICHI;NAKADA, NAOKI;REEL/FRAME:004304/0008
Effective date: 19840727